We looked previously at a partial skull, collected in northern Africa. Apart from the odd outing when it’s been used in teaching, it’s been sat in a box on my desk for a couple of years now, forlornly hoping that it might one day earn a place in the peer-reviewed literature. However, that would only apply if it were a fossil, and as we’ll see that’s contentious.

Anyway, so… what is it?
To begin with, the elongate, pointed rostrum (with stretched premaxillae and maxillae that extend for the entire length of the preserved portion), evidence for a polydont, homodont dentition, enlarged dorsal foramina at the base of the rostrum, laterally extensive maxilla that overhangs the orbit, elevated and retracted nasal region, antorbital notch, and large ventral concavity medial to the orbit (for a massive air sinus) demonstrate that this is a cetacean, an odontocete, and specifically a delphinid. So, yup, it’s definitely a dolphin.

To try and identify it more precisely we need to look at a few details. The premaxillary-maxillary suture line is relatively straight for most of the length of the rostrum, only curving laterally as the rostrum flares outwards as it approaches the antorbital notch. The left premaxilla exhibits only a single foramen. The maxilla tapers at its anterior end but is otherwise of roughly constant width for the length of the rostrum. The small antorbital notch is approximately semi-circular and a small convexity projects laterally from the maxilla at the notch’s anterior margin. Two large anterior foramina and one smaller posterior one are present on the posteromedial part of the maxilla. The dorsal margin of the orbit is approximately semi-circular and the ventral end of the postorbital process is blunt. There are definitely 18 alveoli, and probably 20 (the rostrum’s tip is abraded, making it difficult to be sure). I’ve labelled some of the key bits and pieces in the photos above: the three large maxillary foramina are respectively marked f1, f2 and f3.

Orcininae and Globicephalinae: the presence of a long rostrum rules out further comparison with any of the orcinines or globicephalines (killer whales, pilot whales, false killer whales and kin, all of which have a short, broad rostrum [Orcinus orca shown here]). Peponocephala (the melon-headed whale: it may or may not be a globicephaline (Buchholtz & Schur 2004, May-Collado & Angnarsson 2006)) has particularly large antorbital notches and tooth rows that don’t extend as far along the rostrum as they do in this specimen (Mikkelsen & Sheldrick 1992, Jefferson & Barros 1997).

Steninae: stenine dolphins (humpbacked dolphins, rough-toothed dolphins and tucuxis) can be immediately discounted from comparison as they all possess a more gracile rostrum that has concave margins at the anterior end. The antorbital notches of these dolphins are either V-shaped or very shallow. While I’ve grouped humpbacked dolphins (Sousa) and rough-toothed dolphins (Steno) together here, as per Muizon (1988), some studies (May-Collado & Angnarsson 2006) find Sousa to be a delphinine.

But I’m still not entirely happy. The question I’ve been trying to answer is: which Tursiops species does it belong to, and does it represent a new one? Most people interested in animals know of ‘the Bottlenose dolphin’ Tursiops truncatus. But it’s been argued for a while now that ‘Tursiops truncatus‘ of tradition deserves to be split up again, with offshore and nearshore populations in the Indopacific and Atlantic oceans clearly grouping apart on morphology and genetics (Hoelzel et al. 1998, LeDuc et al. 1999, Wang et al. 1999, Yang et al. 2005 and references therein).

The large, offshore dolphins are now called T. truncatus Montagu, 1821, and the smaller, nearshore ones are T. aduncus Ehrenberg, 1832. T. truncatus is longer-bodied (with 62-67 vertebrae, as opposed to 59-62 in T. aduncus) and has a proportionally shorter rostrum. T. aduncus further differs from T. truncatus in having elongated dark spots on its ventral surface. However, T. aduncus populations from South Africa are highly distinct from so-called T. aduncus populations from Chinese waters, and because the modern use of the name T. aduncus is associated with South African dolphins, Natoli et al. (2004) suggested that the Chinese ‘T. aduncus‘ should warrant recognition as a third species. Given that there are about 20 old Tursiops species names (Hershkovitz 1966), working out which would be the right one to use is not going to be easy [adjacent T. aduncus image from wikipedia].

Furthermore, it now seems that T. aduncus and T. truncatus aren’t close relatives anyway, with T. aduncus being outside a clade that includes T. truncatus, Stenella and Delphinus (LeDuc et al. 1999, Yang et al. 2005). I really hope that this is supported by further studies, as it means that T. aduncus will deserve its own genus: this’ll be the first new extant cetacean genus named since Australophocaena was coined in 1985.

Anyway, with the literature and lots of specimen photos to hand I had a bash at identifying the African Tursiops skull. Wang et al. (2000) included a key on how to differentiate the skulls of T. aduncus and T. truncatus. Unfortunately, you need to know the shape and position of the premaxillary convexity, and also the complete skull length, to get the measurements you need, and the specimen isn’t complete enough for that (frustratingly, a chunk of the premaxilla is missing just where the premaxillary convexity should be… the convexity is usually particularly prominent in T. aduncus). However, the fact that the premaxillary-maxillary suture is not laterally concave (‘pinched in’) suggests that the skull is T. truncatus.

Fossil bottlenose dolphins that aren’t

But there are fossil species to take account of too if, that is, the African specimen is a fossil. I was told that it was (I believe it comes from a place where the Pleistocene fossils are white) and have assumed this to be correct, though I do know that worn and battered cetacean bones can look like fossils even when they aren’t. This has now been challenged, and I’ll need to chase things up to find out either way [UPDATE: it was literally dug out of the ground, not picked up from the surface as I said previously]. Anyway, whatever, quite a few fossil Tursiops have been named, including T. cortesii (Fischer, 1829), T. brochii Capellini, 1863, T. capellinii Del Prato, 1897, T. astensis Sacco, 1891, T. ossennae Simonelli, 1911 and T. oligodon Pilleri & Siber, 1989.

Pilleri (1987) regarded T. capellinii, T. brochii and T. cortesii, all from the Pliocene of Italy, as ‘representatives of the same chronospecies’ (in which case T. cortesii is the correct name), and it now seems that T. cortesii and also T. oligodon from the Pliocene Pisco Formation of Peru aren’t Tursiops at all, but should in fact be recognised as Hemisyntrachelus (T. cortesii is the type species of this genus: it’s an unusual delphinid and might be an orcinine) (Bianucci 1996, Post & Bosselaers 2005). T. ossennae from the Pleistocene seems to be the only valid extinct Tursiops still recognised (Bianucci 1996), but I haven’t seen any figures of it and don’t know what it looks like.

For now, this is where it ends. And this might be another of those ‘must convert this into a technical paper at some stage’ blog posts. You know, like what all the other bloggers do…

Comments

Awww nooo! This is the first time I’ve ever got one of your id quiz’s right and I didn’t bother commenting as I thought it was probably some obscure fossil I knew nothing about and not the bottlenose it looked just like! Gah.

Mildly interesting bit of trivia on bottlenose skulls is that there was a bit of a kerfuffle in lincolnshire near my previous abode when someone turned one up about 20 miles inland and various cryptozoological suggestions were offered before the truth was established. Then the mystery became how it got there (I just assumed a tribe of marshdwelling fenlanders had brought a stranding back to the village to tuck into).

Wow… I never quite expected an old dolphin skull to prove to be so fascinating to me. Cetacean diversity is one aspect that always gets me really excited, considering how we seem to be finding ‘new’ species hidden among supposedly familiar species every now and then. There were the short-beaked and long-beaked common dolphins (Delphinus), the tucuxi and costero (Sotalia), the Irrawaddy and Australian snubfin (Orcaella), not to mention that Bryde’s whale and minke whale comprise of at least 2 distinct species each, and don’t get me started on Omura’s whale…

Ah yes… the old problem of how to differentiate the two bottlenose dolphin species. I’ve pretty much given up trying to tell them apart based on photographs alone.

I was under the impression that T. aduncus is an inshore Indo-Pacific species, and so includes among them the famous habituated dolphins of Shark Bay, Australia. I am led to understand that elsewhere, such as in the Atlantic and East Pacific, both the inshore and offshore bottlenose dolphins are T. truncatus.

And like Andreas Johansson, I am seriously confused as to the identity of captive dolphins, given that a large number of them are caught in the wild in the Indo-Pacific and then shipped to North American oceanariums. It would be interesting to find out if some of these captives are T. aduncus, which would raise interesting questions on the provenance of our captive dolphins, and to see if hybridisation has taken place between captive T. truncatus and T. aduncus. (Maybe that’s a possible contributing factor as to why they don’t seem to breed so well in captivity!)

Well this is the first time Ive even been close to getting it right! Interesting stuff.

While on the subject of identifing bones, I found the ones shown here in barn owl pellets. CAn anyone help with the mystery bone and the bottom (and I’m not 100% sure on the others. Im afraid Im used to seeing small mamals with fur and flesh still present!)

“Remind me…did the Chinese River dolphin have an asymetic skull? I seem to remember reading something somewhere.”

Lipotes has a slightly asymmetrical skull. There aren’t very many odontocetes with symmetrical skulls – some examples are extant phocoenids, the Fransiscana (Pontoporia) and… I can’t think of any other exant examples (there may be a couple).

In any event, here’s the short answer: the right side of the facial region is much larger because the right nasal passage is adapted for sound production, while the left nasal passage is more or less unmodified (with regards to sound production) and retained for breathing.

I don’t really know whether or not its a fossil (would want to see it in person) – and the original discoverer is certainly going to be your best source of info. I would just say that depending on where it was found, it doesn’t have to be a fossil. Could have been dug out of Recent sediments on the beach for example (there are plenty plenty of places on the coast with Recent sediments and cliffs of Pleistocene exposure all around the world). It certainly does look like a weather-worn modern specimen though.

— Hai-Ren says ‘I am led to understand that elsewhere, such as in the Atlantic and East Pacific, both the inshore and offshore bottlenose dolphins are T. truncatus‘. Yes, some studies report that both nearshore and offshore Tursiops populations in the Atlantic are T. truncatus (e.g., Kingston & Rosel 2004, Segura et al. 2006). Kingston & Rosel (2004) found these two morphotypes to be more distinct genetically than two Delphinus species, and both were distinct from T. aduncus. Coastal Tursiops from the UK (including the extinct Humbar River estuary population) have been identified as T. truncatus (Nichols et al. 2007). However, Hoelzel et al. (1998) had indicated that the nearshore Tursiops from the Atlantic were T. aduncus, which is what I had in mind when saying that the presence of T. aduncus had been demonstrated in the Atlantic. I may change the wording.

— Re: ‘blogging on peer-reviewed research’, I decided when I first learnt about this not to participate. Not because I don’t think it’s an excellent idea, but because all I do is blog on peer-reviewed research: Tet Zoo is, pretty much, not like other blogs. Your insight serves you well. Bury your feelings deep down, Matt. They do you credit, but they could be made to serve the Emperor.

— Finally, is the specimen a fossil or not? Its discoverer (Dave Martill) extracted it from clay sediment and regards it as a fossil. However, I learnt in discussion with him today that he holds a particularly controversial view of what a fossil is, and essentially regards anything naturally entombed in sediment as a fossil. I can see that it’s difficult to provide a clear definition of a fossil (given that mineralization, or loss of organic content, is not a criterion, and that the fossilisation process is a continuum), but I don’t think I can agree. At most, the specimen is thousands of years old.

@Boesse: I’m at the Calvert Marinue Museum in Maryland, USA. I’m presently wrapping project on a cetacean rib with shark predation trauma and starting one on an unidentified pontoporiid rostrum. Where/what are you working?

Ah, another Tet Zoo special week to look forward to. I would suggest that all cetacean skulls are a bit weird. Are you only covering extant forms, or also some of the fossil ones? Among the fossil forms are ‘dolphins’ pretneding to be walruses and others pretending to be sharks – and we have of course our extant ‘dolphin’ pretending to be an unicorn.

You mention turning this into a technical paper – I see you also turn some of your blog material into popular articles – I just read (well last night actually) your Fortean Times article on Intelligent Dinosaurs. Nicely written – though I would take issue with two points:
1. You state “people who regard the humanoid shape as somehow inevitable often hold religious convictions.” I have to say that has not been my experience. I guess that your not talking about Creationists (who would tend to disagree that dinosaurs would evolve into anything!)- but rather persons who have a teleological view of evolution, like Teilhard de Chardin. Still even then I’m not sure I could agree that there is such a pattern.
2. You refer at the end to the ‘Avisapiens’ as having an “element of biological plausibility”. It is certainly less contrived than the other ‘reconstructions’, but is it plausible, Im afraid I must disagree.

Notwithstanding these 2 quibbles (that’s a lovely word – defined as ‘a petty distinction or an irrelevant objection’) – it was a thoroughly enjoyable read which obviously drew on your blog on the same subject.

As an aside, what do you think of the Irish ‘nail-tailed’ wildcat referred to in another article in the same issue?

By the way Darren, thanks for your blog, a new Tet Zoo article always makes my day!

Bobk, I’m working with pinnipeds and cetaceans from the Purisima Formation of central California. As far as cetaceans go, right now I’m primarily working with some phocoenid fossils, and the bizarre mysticete Herpetocetus. I take it you’ve already read Godfrey and Barnes 2008, on the new St. Marys Fm. pontoporiid?

Yes, I have read it; actually Godfrey is my boss/advisor at the museum. It would be great if the rostrum I’m working with goes with that new pontoporiid, but I don’t think one could conclusively say. By the way, the rib is from the Yorktown Formation of North Carolina, and the rostrum is from the St. Mary’s Formation of Maryland.

I, for one, couldn’t agree more. It *unfortunately* means that fossils so defined could only be a few hundred years old… However, this I believe is the definition that most agrees with the principle of uniformitarianism. I do like the use of the term subfossil as a good compromise. However, being familiar with much of Dave Martill’s taphonomic work, I understand using geologic/taphonomic/uniformitarian logic rather than invoking some magical cutoff age.

Am pleased to see that my Fortean Times article is out, though haven’t seen it yet. Yes, it evolved out of stuff you’ve previously read on Tet Zoo. Incidentally, there is also a kid’s TV series on big-brained dinosaurs being broadcast here in the UK (infuriating title = Dinosapien): I would love to know if it also owes its origins to Tet Zoo, but have yet to find this out.

1. You state “people who regard the humanoid shape as somehow inevitable often hold religious convictions.” I have to say that has not been my experience. I guess that your not talking about Creationists (who would tend to disagree that dinosaurs would evolve into anything!)- but rather persons who have a teleological view of evolution, like Teilhard de Chardin. Still even then I’m not sure I could agree that there is such a pattern.

Hmm, maybe I should have been more specific: those scientists who have expressed the opinion that the humanoid body shape is somehow inevitable do indeed seem to hold religious convictions.

2. You refer at the end to the ‘Avisapiens’ as having an “element of biological plausibility”. It is certainly less contrived than the other ‘reconstructions’, but is it plausible, Im afraid I must disagree.

Well, that’s your opinion. I would argue that it does indeed have an ‘element of biological plausibility’ (which is not the same as saying ‘it is plausible’!).

As an aside, what do you think of the Irish ‘nail-tailed’ wildcat referred to in another article in the same issue?

Again, I haven’t seen the article yet, but I already know quite a lot about the subject as the author (Gary Cunningham) is a good friend of mine and we often talk about Irish wildcats. My take on this has been that the ‘Irish wildcat’ reports were too vague to be informative and did not convincingly refer to a small cat. That’s still the case so far as I know but we now know that wildcats were indeed present in Ireland in the Holocene (mentioned here), so it’s conceivable that they hung on there until modern times.

Returning to dolphin skulls, David wrote…

The official definition of “fossil” is “more than 10,000 years old”. Anything younger is a subfossil. Of course this doesn’t always make sense in terms of the state of preservation.

Dave Martill tells me that this is completely arbitrary and not helpful, given that there isn’t one magical cutoff point at which ‘fossilisation’ begins. I have no strong opinion on this either way and want to learn more.